1. Field of the Invention
The present invention relates to a sewn airbag and also to a method for producing the same. It particularly relates to an invention suitable for reinforcement in a region of a sewn airbag where reinforcement is required (e.g., a peripheral sewn region of an airbag made of an outer panel and an inner panel sewn together).
In the following description, airbags for knee protection or side impact will be mainly described as examples. The invention is not particularly limited as long as it is a sewn airbag having a sewn region, and can be applied to airbags for the driver seat, front passenger seat, etc.
In the specification of the present application, a cover factor (hereinafter sometimes abbreviated to “CF”) is determined by the following equation (1).CF=NW×DW0.5+NF×DF0.5   (1)wherein
NW: warp density (the number of yarns/inch), DW: warp fineness (dtex)
NF: weft density (the number of yarns/inch), DF: weft fineness (dtex)
“Part” that indicates a unit of blending, etc., is by mass unless otherwise noted.
2. Description of the Related Art
In automobiles, airbag devices for passenger protection are mounted. As airbag base fabrics to be incorporated into an airbag device, cloths formed by weaving (e.g., plain-weaving) fiber yarns (e.g., polyamide fibers, polyester fibers) are used.
The purpose of an airbag is to protect the passengers of the automobile. As the basic performance, an airbag is required to have air-blocking performance (low breathability) so that it can inflate instantly and retain the air pressure for a sufficient period of time.
Then, in the case of an airbag for knee protection or side impact, the volume for inflation is low, and the gas pressure tends to be high upon the operation of the inflator. Therefore, for such airbags, in order to ensure pressure resistance, a high-density coated base fabric having high CF has been used, or a reinforcing fabric has been sewn together with a sewn region that is likely to receive pressure, for example.
However, recently, also for such airbags for knee protection or side impact, the development of a sewn airbag with more simple reinforcement, which leads to the further reduction of airbag weight or resource saving, and also leads to the reduction of man-hours, has been desired.
In order to meet these demands, JP-A-2005-138704 proposes a technique of using base fabrics having relatively small CF and also using a thick yarn as a sewing yarn (e.g., yarn count of 20 (600 dtex) or more) to reinforce the sewn region (to increase pressure resistance).
However, in this technique, because a thick yarn is used as a sewing yarn, outgassing often happens at the seam. In order to prevent outgassing, JP-A-2005-138704 further describes, in paragraph 0018, that an anti-outgassing material is given to the sewn region. In the paragraph, it is described that in order to prevent outgassing, on the upper surface and/or lower surface of a peripheral sewn region, 1) various seal materials, adhesive materials, and pressure-sensitive adhesive materials, such as silicone-based, polyurethane-based, epoxy-based, acrylic-based, vinyl-based, and halogen-containing resins and rubbers, are applied, sprayed, or laminated, 2) an adhesive cloth, a pressure-sensitive adhesive cloth, or the like is attached, or 3) a main base fabric and a separate protection cloth are placed on top of each other and sewn together.
The anti-outgassing material described therein has a possibility of sewn region reinforcement. However, unlike the invention of the present application (as will be described later), it is not intended to increase the slippage resistance of the base fabrics forming the airbag body to reinforce the sewn region.
In addition, in the case of 1), it is likely that a relatively large amount of seal material or the like is necessary to prevent outgassing from the seam. The application of a large amount of seal material to a sewn region does not lead to resource saving or airbag weight reduction, and also adversely affects the folding properties of the airbag.
In addition, when an anti-outgassing material is given to a sewn region, not just in the cases of 2) and 3), but also in the case of 1) where an anti-outgassing material is applied, etc., the application step is not intended to be performed synchronously with a sewing step and a prevention material curing step. Accordingly, this does not lead to the reduction of production man-hours.
Further, JP-A-2010-241417 discloses the following invention: in a curtain airbag, a bead made of a seal material or the like is formed along the high-pressure side of the first seam portion toward or facing the flowing gas, thereby reinforcing the seam portion (paragraph 0015). However, the bead is not directly applied and formed onto the first seam, but is applied and formed along the high-pressure side. Thus, a coating film is not directly formed on a sewn region like the present invention.
JP-A-2010-234909 discloses the following invention: in order to improve the airtightness of the joining portion of a curtain airbag, an adhesive is applied along the inner joining portion of a sewn region of the curtain airbag, then a non-application part is formed, and the non-application part is sewn (Abstract, etc.). However, the adhesive is applied to a region to be sewn inside between the facing surfaces of base fabrics before sewing. Thus, it is not formed outside a sewn region after sewing like the present invention.